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c/coa·submitted 2 years ago by u/tomas_lehtinen

[Discussion] related substances are doing more work than we give it credit for

Discussionbranch of 11 comments

related substances are doing more work than we give it credit for, and I am aware this is a minority view on this board. Sent one vial to VendorInvestigate and Janoshik. 98.9% and a claimed 98.0%. Cost me more than the vial and I would do it again. The PDF creation date being later than the analysis date is usually a…

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11 comments, started 2 years ago
u/valeria_karlsen384 points·2 years ago

Water content 3.8%, acetate 6.2%, purity 99%, net peptide about 90% of label weight. All four numbers honest, and I had to read it twice.

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u/camila_lindqvist312 points·2 years ago

Water content 3.8%, acetate 6.2%, purity 99%, net peptide about 90% of label weight.

valeria_karlsen has the distinction right — one is a fraction of the detector signal, the other is a fraction of the mass.

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u/anders_kuusela421 points·2 years ago

My first certificate had a compound name, a percentage and a logo. I thought that was normal. It is not, and now I know what to ask for.

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u/liv_nkemelu107 points·2 years ago

Are the related substances itemised or is it a single total?

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u/valeria_karlsen268 points·2 years ago

Disagree that a lower number is automatically worse. A conservative claim that survives testing is worth more than an optimistic one that does not.

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u/cesar_ivaturi202 points·2 years ago

area% is not mass%, and the difference is the whole game

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u/dario_boateng303 points·2 years ago

water content is on there and everyone skips it

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u/amara_halonen247 points·2 years ago

batch number, date of analysis, method, individual impurities — that is the minimum set

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u/tomas_lehtinenOP124 points·2 years ago·edited

Small fix — 214nm, not 280nm. It matters here because the impurity you are asking about barely absorbs at the longer wavelength.

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u/foam_head_fred182 points·2 years ago

batch number, date of analysis, method, individual impurities — that is the minimum set

Adding the bit that always gets missed: the lot on the vial has to match the lot on the page, or none of this applies to your material.

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u/ghrp_history-34 points·2 years ago

Did you get the chromatogram or only the summary line?

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About c/coa

How to read a certificate of analysis and what it does and does not tell you. Area% versus mass%, identity versus quantity, water content, related substances, acetate counterions, and the difference between a vendor-supplied COA and an independent test on the vial you actually received.

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